- Email: [email protected]
Follow-up in obese pregnant women to prevent stillbirth
Letters to the Editors
www.AJOG.org
TABLE
Comparison of pooled results from original results and revised results that include data from Pandis et al3 Outcome
Likelihood ratio of positive test (95% CI)
Likelihood ratio of negative test (95% CI)
Sensitivity (95% CI)
Specificity (95% CI)
Successful induction
.......................................................................................................................................................................................................................................................................................................................................................................
Original results
1.66 (1.20-2.31)
0.51 (0.39-0.67)
64.0 (57.3-71.6)
64.6 (55.1-75.7)
Revised results
1.71 (1.23-2.38)
0.49 (0.37-0.65)
66.0 (59.9-72.8)
64.5 (55.3-75.1)
....................................................................................................................................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................................................................................................................................................
Vaginal delivery ⬍24 hr
.......................................................................................................................................................................................................................................................................................................................................................................
Original results
1.83 (1.23-2.74)
0.51 (0.31-0.84)
59.2 (46.0-76.0)
64.9 (48.2-87.3)
Revised results
1.91 (1.36-2.68)
0.44 (0.24-0.81)
66.6 (56.8-78.2)
64.6 (49.9-83.6)
.......................................................................................................................................................................................................................................................................................................................................................................
Although the authors of the letter oppose synthesizing the data with likelihood ratios, these measures of diagnostic accuracy are deemed the best way to summarize the accuracy of clinical tests and are more powerful than sensitivities and specificities.5 Although we pooled likelihood ratios through weighted averages using a random-effects model, the authors of the letter could not replicate our values because they handled the data as if they were from a single study. Finally, the summary receiver operating characteristics analysis was presented in Table 2 of our original article. Ann S. Hatfield, MD Luis Sanchez-Ramos, MD Andrew M. Kaunitz, MD Department of Obstetrics and Gynecology University of Florida College of Medicine–Jacksonville 655 West 8th St Jacksonville, FL 32209 [email protected]
REFERENCES 1. Rane SM, Pandis GK, Guirgis RR, Higgins B, Nicolaides KH. Preinduction sonographic measurement of cervical length in prolonged pregnancy: the effect of parity in the prediction of induction-to-delivery interval. Ultrasound Obstet Gynecol 2003;22:40-4. 2. Rane SM, Guirgis RR, Higgins B, Nicolaides KH. Models for the prediction of successful induction of labor based on pre-induction sonographic measurement of cervical length. J Matern Fetal Neonatal Med 2005;17:315-22. 3. Pandis GK, Papageorghiou AT, Otigbah CM, Howard RJ, Nicolaides KH. Randomized study of vaginal misoprostol (PGE1) and dinoprostone gel (PGE2) for induction of labor at term. Ultrasound Obstet Gynecol 2001;18:629-35. 4. Boozarjomehri F, Timor-Tritsch I, Chao CR, Fox HE. Transvaginal ultrasonographic evaluation of the cervix before labor: presence of cervical wedging is associated with shorter duration of induced labor. Am J Obstet Gynecol 1994;171:1081-7. 5. Honest H, Khan KS. Reporting measures of accuracy in systematic reviews of diagnostic literature. BMC Health Serv Res 2002;2:4. Published by Mosby, Inc. doi: 10.1016/j.ajog.2008.02.040
Follow-up in obese pregnant women to prevent stillbirth TO THE EDITORS: We have read the article by Chu et al entitled “Maternal obesity and risk of stillbirth: a meta-analysis” in the September issue of the Journal with great interest.1 We want to share our appreciation that the “Editors’ Choice”– label was given to an article on complications of what is probably the greatest challenge in the future of obstetrics (ie, obesity), which so far has not received the attention it deserves in the obstetric literature. We also want to congratulate the authors for the quality of their work and the importance of their findings. Based on a metaanalysis of 9 high-quality studies, they found the unadjusted odds ratios of a stillbirth were 1.47 (95% CI, 1.08-1.94) and 2.07 (95% CI, 1.59-2.74) in overweight and obese women, respectively. We do not fully agree, however, with their tentative explanation of their findings. Although they concentrate on a biologic pathway to try to explain the excess in stillbirth (increased risk for diabetes mellitus, hypertension, and hyperlipidemia), the authors strangely fail to
mention the huge difference in the quality of the obstetric follow-up in obese pregnant women. Furthermore, no clinical advice or lesson is drawn from the data. Indeed, it is known that obese pregnant women are attending less antenatal clinics and that the clinical indicators of fetal well-being and adequate growth (eg, fundal height, fetal movements, weight gain) are less accurate.2 As a result, the clinician of obese pregnant mothers is more dependent on technical means for fetal monitoring, especially ultrasound examination, than is the clinician of normal weight mothers. There is strong evidence to demonstrate that the continuous improvement of the quality of the ultrasound equipment is barely sufficient to keep pace with the growing layer of subcutaneous fat of the average obstetric patient.3 As a result, malformations that increase the risk of stillbirth, such as cardiac malformations, are often missed in these patients. Growth estimations also are less accurate. The same probably applies to antepartum JULY 2008 American Journal of Obstetrics & Gynecology
e17
Letters to the Editors and intrapartum cardiotocography. This knowledge, together with the findings of this important study should cause obstetricians to consider an adapted, more intensive scheme for pregnancy follow-up in overweight and obese pregnant women. So far, this has not been echoed in guidelines on the subject. We feel the study missed the opportunity to highlight these needs. Roland Devlieger, MD, PhD Department of Obstetrics and Gynecology University Hospitals Leuven Herestraat 49 B-3000 Leuven, Belgium [email protected] Isabelle Guelinckx, MSc Margareta Vansant, PhD Department of Nutrition—Preventive Medicine Leuven Food and Nutrition Research Center (LFoRCe) Leuven, Belgium REFERENCES
www.AJOG.org procedures may be more difficult in obese pregnant women, which can result in less complete prenatal ascertainment of congenital anomalies, fetal growth abnormalities, and other conditions that are associated with a hostile intrauterine environment. These missed diagnoses may explain some of the increased rate of stillbirth that is associated with obesity during pregnancy. Management of pregnancy in obese women not only calls for more intense monitoring of the fetus but also should involve more intense monitoring for gestational diabetes mellitus and pregnancy-induced hypertension and preparation for increased risks of anesthesia complications, wound disruption, infection, and deep venous thrombophlebitis.1 A recent estimate that approximately 22% of pregnant women in 9 states are obese suggests that obese women account for nearly 1 million of the approximately 4 million annual births int the United States.2 Given that obesity is now a common complication of pregnancy, we strongly support the call of Devlieger et al for guidelines that more specifically and in greater detail address the management of obesity in pregnancy.
1. Chu SY, Kim SY, Lau J, et al. Maternal obesity and risk of stillbirth: a metaanalysis. Am J Obstet Gynecol 2007;197:223-8. 2. Mighty HE, Fahey AJ. Obesity and pregnancy complications. Curr Diab Rep 2007;7:289-94. 3. Hendler I, Blackwell SC, Treadwell MC, Bujold E, Sokol RJ, Sorokin Y. Does advanced ultrasound equipment improve the adequacy of ultrasound visualization of fetal cardiac structures in the obese gravid woman? Am J Obstet Gynecol 2004;190:1616-9.
Susan Y. Chu, PhD, MSPH William M. Callaghan, MD, MPH Shin Y. Kim, MPH Division of Reproductive Health Centers for Disease Control and Prevention, MS K-23 Atlanta, GA 30333
© 2008 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2008.02.037
REFERENCES
REPLY We appreciate the interest and comments of Devlieger et al on our article, “Maternal obesity and the risk of stillbirth: A metaanalysis.” We agree that ultrasonography and other diagnostic
1. Catalano PM. Management of obesity in pregnancy. Obstet Gynecol 2007;109:419-33. 2. Kim SY, Dietz PM, England L, Morrow B, Callaghan WM. Trends in prepregnancy obesity in nine states, 1993-2003. Obesity 2007; 15:968-73. Published by Mosby, Inc. doi: 10.1016/j.ajog.2008.02.038
The benefits of customizing for maternal factors or the benefits of using an intrauterine standard at preterm ages? TO THE EDITORS: We applaud Groom et al1 for their recent work to better understand the properties of customized birthweight percentiles. However, their conclusions that their findings “highlight the important contribution of maternal factors to fetal size” and “reinforce the importance of using customized birthweight centiles when classifying infants as small for gestational age (SGA), in particular when considering preterm births” deserve further consideration. It is important to recognize that there are 2 differences between the customized and population standards at preterm ages: (1) the customized percentiles include a regression-based adjustment for maternal factors that are associated with birthweight (ie, the “customization” to identify babies expected to be “small-but-healthy”), and (2) the customized percentiles use an intrauterine stane18
American Journal of Obstetrics & Gynecology JULY 2008
dard (via backward extrapolation of Hadlock’s in utero standard2), in contrast to the population reference that is based on the distribution of live births. To conclude correctly that their observed results were due to correcting for maternal factors and NOT simply due to using a population reference that was derived from the weights of fetuses in utero (irrespective of customization), the authors would have needed to use an intrauterine population standard for comparison. As the authors point out themselves, the use of conventional population references at preterm ages is likely biased because of the high number of preterm births that may also be growth restricted. The percentages of preterm infants who are identified as SGA by the customized standard reported by Groom et al1 (Table 1) are highly similar to the percentages that are obtained
www.AJOG.org
TABLE
Comparison of pooled results from original results and revised results that include data from Pandis et al3 Outcome
Likelihood ratio of positive test (95% CI)
Likelihood ratio of negative test (95% CI)
Sensitivity (95% CI)
Specificity (95% CI)
Successful induction
.......................................................................................................................................................................................................................................................................................................................................................................
Original results
1.66 (1.20-2.31)
0.51 (0.39-0.67)
64.0 (57.3-71.6)
64.6 (55.1-75.7)
Revised results
1.71 (1.23-2.38)
0.49 (0.37-0.65)
66.0 (59.9-72.8)
64.5 (55.3-75.1)
....................................................................................................................................................................................................................................................................................................................................................................... ................................................................................................................................................................................................................................................................................................................................................................................
Vaginal delivery ⬍24 hr
.......................................................................................................................................................................................................................................................................................................................................................................
Original results
1.83 (1.23-2.74)
0.51 (0.31-0.84)
59.2 (46.0-76.0)
64.9 (48.2-87.3)
Revised results
1.91 (1.36-2.68)
0.44 (0.24-0.81)
66.6 (56.8-78.2)
64.6 (49.9-83.6)
.......................................................................................................................................................................................................................................................................................................................................................................
Although the authors of the letter oppose synthesizing the data with likelihood ratios, these measures of diagnostic accuracy are deemed the best way to summarize the accuracy of clinical tests and are more powerful than sensitivities and specificities.5 Although we pooled likelihood ratios through weighted averages using a random-effects model, the authors of the letter could not replicate our values because they handled the data as if they were from a single study. Finally, the summary receiver operating characteristics analysis was presented in Table 2 of our original article. Ann S. Hatfield, MD Luis Sanchez-Ramos, MD Andrew M. Kaunitz, MD Department of Obstetrics and Gynecology University of Florida College of Medicine–Jacksonville 655 West 8th St Jacksonville, FL 32209 [email protected]
REFERENCES 1. Rane SM, Pandis GK, Guirgis RR, Higgins B, Nicolaides KH. Preinduction sonographic measurement of cervical length in prolonged pregnancy: the effect of parity in the prediction of induction-to-delivery interval. Ultrasound Obstet Gynecol 2003;22:40-4. 2. Rane SM, Guirgis RR, Higgins B, Nicolaides KH. Models for the prediction of successful induction of labor based on pre-induction sonographic measurement of cervical length. J Matern Fetal Neonatal Med 2005;17:315-22. 3. Pandis GK, Papageorghiou AT, Otigbah CM, Howard RJ, Nicolaides KH. Randomized study of vaginal misoprostol (PGE1) and dinoprostone gel (PGE2) for induction of labor at term. Ultrasound Obstet Gynecol 2001;18:629-35. 4. Boozarjomehri F, Timor-Tritsch I, Chao CR, Fox HE. Transvaginal ultrasonographic evaluation of the cervix before labor: presence of cervical wedging is associated with shorter duration of induced labor. Am J Obstet Gynecol 1994;171:1081-7. 5. Honest H, Khan KS. Reporting measures of accuracy in systematic reviews of diagnostic literature. BMC Health Serv Res 2002;2:4. Published by Mosby, Inc. doi: 10.1016/j.ajog.2008.02.040
Follow-up in obese pregnant women to prevent stillbirth TO THE EDITORS: We have read the article by Chu et al entitled “Maternal obesity and risk of stillbirth: a meta-analysis” in the September issue of the Journal with great interest.1 We want to share our appreciation that the “Editors’ Choice”– label was given to an article on complications of what is probably the greatest challenge in the future of obstetrics (ie, obesity), which so far has not received the attention it deserves in the obstetric literature. We also want to congratulate the authors for the quality of their work and the importance of their findings. Based on a metaanalysis of 9 high-quality studies, they found the unadjusted odds ratios of a stillbirth were 1.47 (95% CI, 1.08-1.94) and 2.07 (95% CI, 1.59-2.74) in overweight and obese women, respectively. We do not fully agree, however, with their tentative explanation of their findings. Although they concentrate on a biologic pathway to try to explain the excess in stillbirth (increased risk for diabetes mellitus, hypertension, and hyperlipidemia), the authors strangely fail to
mention the huge difference in the quality of the obstetric follow-up in obese pregnant women. Furthermore, no clinical advice or lesson is drawn from the data. Indeed, it is known that obese pregnant women are attending less antenatal clinics and that the clinical indicators of fetal well-being and adequate growth (eg, fundal height, fetal movements, weight gain) are less accurate.2 As a result, the clinician of obese pregnant mothers is more dependent on technical means for fetal monitoring, especially ultrasound examination, than is the clinician of normal weight mothers. There is strong evidence to demonstrate that the continuous improvement of the quality of the ultrasound equipment is barely sufficient to keep pace with the growing layer of subcutaneous fat of the average obstetric patient.3 As a result, malformations that increase the risk of stillbirth, such as cardiac malformations, are often missed in these patients. Growth estimations also are less accurate. The same probably applies to antepartum JULY 2008 American Journal of Obstetrics & Gynecology
e17
Letters to the Editors and intrapartum cardiotocography. This knowledge, together with the findings of this important study should cause obstetricians to consider an adapted, more intensive scheme for pregnancy follow-up in overweight and obese pregnant women. So far, this has not been echoed in guidelines on the subject. We feel the study missed the opportunity to highlight these needs. Roland Devlieger, MD, PhD Department of Obstetrics and Gynecology University Hospitals Leuven Herestraat 49 B-3000 Leuven, Belgium [email protected] Isabelle Guelinckx, MSc Margareta Vansant, PhD Department of Nutrition—Preventive Medicine Leuven Food and Nutrition Research Center (LFoRCe) Leuven, Belgium REFERENCES
www.AJOG.org procedures may be more difficult in obese pregnant women, which can result in less complete prenatal ascertainment of congenital anomalies, fetal growth abnormalities, and other conditions that are associated with a hostile intrauterine environment. These missed diagnoses may explain some of the increased rate of stillbirth that is associated with obesity during pregnancy. Management of pregnancy in obese women not only calls for more intense monitoring of the fetus but also should involve more intense monitoring for gestational diabetes mellitus and pregnancy-induced hypertension and preparation for increased risks of anesthesia complications, wound disruption, infection, and deep venous thrombophlebitis.1 A recent estimate that approximately 22% of pregnant women in 9 states are obese suggests that obese women account for nearly 1 million of the approximately 4 million annual births int the United States.2 Given that obesity is now a common complication of pregnancy, we strongly support the call of Devlieger et al for guidelines that more specifically and in greater detail address the management of obesity in pregnancy.
1. Chu SY, Kim SY, Lau J, et al. Maternal obesity and risk of stillbirth: a metaanalysis. Am J Obstet Gynecol 2007;197:223-8. 2. Mighty HE, Fahey AJ. Obesity and pregnancy complications. Curr Diab Rep 2007;7:289-94. 3. Hendler I, Blackwell SC, Treadwell MC, Bujold E, Sokol RJ, Sorokin Y. Does advanced ultrasound equipment improve the adequacy of ultrasound visualization of fetal cardiac structures in the obese gravid woman? Am J Obstet Gynecol 2004;190:1616-9.
Susan Y. Chu, PhD, MSPH William M. Callaghan, MD, MPH Shin Y. Kim, MPH Division of Reproductive Health Centers for Disease Control and Prevention, MS K-23 Atlanta, GA 30333
© 2008 Mosby, Inc. All rights reserved. doi: 10.1016/j.ajog.2008.02.037
REFERENCES
REPLY We appreciate the interest and comments of Devlieger et al on our article, “Maternal obesity and the risk of stillbirth: A metaanalysis.” We agree that ultrasonography and other diagnostic
1. Catalano PM. Management of obesity in pregnancy. Obstet Gynecol 2007;109:419-33. 2. Kim SY, Dietz PM, England L, Morrow B, Callaghan WM. Trends in prepregnancy obesity in nine states, 1993-2003. Obesity 2007; 15:968-73. Published by Mosby, Inc. doi: 10.1016/j.ajog.2008.02.038
The benefits of customizing for maternal factors or the benefits of using an intrauterine standard at preterm ages? TO THE EDITORS: We applaud Groom et al1 for their recent work to better understand the properties of customized birthweight percentiles. However, their conclusions that their findings “highlight the important contribution of maternal factors to fetal size” and “reinforce the importance of using customized birthweight centiles when classifying infants as small for gestational age (SGA), in particular when considering preterm births” deserve further consideration. It is important to recognize that there are 2 differences between the customized and population standards at preterm ages: (1) the customized percentiles include a regression-based adjustment for maternal factors that are associated with birthweight (ie, the “customization” to identify babies expected to be “small-but-healthy”), and (2) the customized percentiles use an intrauterine stane18
American Journal of Obstetrics & Gynecology JULY 2008
dard (via backward extrapolation of Hadlock’s in utero standard2), in contrast to the population reference that is based on the distribution of live births. To conclude correctly that their observed results were due to correcting for maternal factors and NOT simply due to using a population reference that was derived from the weights of fetuses in utero (irrespective of customization), the authors would have needed to use an intrauterine population standard for comparison. As the authors point out themselves, the use of conventional population references at preterm ages is likely biased because of the high number of preterm births that may also be growth restricted. The percentages of preterm infants who are identified as SGA by the customized standard reported by Groom et al1 (Table 1) are highly similar to the percentages that are obtained